Trophic ecology of citrus pests based on stable isotope analysis

Macrodactylus pumilio Burm. (Coleoptera: Scarabeidae) and Naupactus cervinus (Boh.) (Coleoptera: Curculionidae) are considered primary pests in citrus crops in Brazil, causing damage to plants and decreasing productivity. However, few studies investigate the ecology of these insects. In this context, the use of stable isotopes analysis (SIA) emerges as an alternative technique to conventional studies of behavioral ecology because it is faster and may explain feeding behavior based on the food source for each species. Field sampling and laboratory experiments were carried out to examine the changes of carbon and nitrogen stable isotope ratios (delta C-13 and delta N-15) among pests and host plants (C-3 citrus and C-4 grasses), providing means to examine trophic interactions. Beetles were collected at the municipality of Gaviao Peixoto, Sao Paulo State, identified and kept at 5 degrees C in saturated saline solution until the SIA. Two patterns for both species were found: delta C-13 value for N. cervinus was -23.6 parts per thousand and -13 parts per thousand for M. pumilio, indicating similarity between the results of delta C-13 of N. cervinus and citrus plants (-26 parts per thousand) and dependence on grasses (-12 parts per thousand) for M. pumilio individuals. The mean delta N-15 value was 4.3 and 5.8 parts per thousand for citrus plants and grass leaves, respectively, and the mean delta N-15 value was 4.456 for N. cervinus and 4.9 parts per thousand for M. pumilio. The results showed a higher affinity of N. cervinus for citrus roots since the larval stage compared with the alternative diet on M. pumilio.